Interpretive Summary: Cheatgrass (Bromus tectorum) is a highly invasive exotic annual grass that has invaded millions of acres of rangelands throughout the Intermountain Western United States. Cheatgrass provides an early maturing fine textured fuel that increases the chance, rate, spread and season of wildfire. Cheatgrass also out competes native perennial seedlings for moisture and therefore truncates succession. As little as 4 cheatgrass plants per square foot can out compete native perennial species, it is not uncommon to virtually have hundreds of cheatgrass plants per square foot. It is also estimated that there may be as much as three times the amount of cheatgrass in the seedbank than that year’s standing crop. It is critical for resource managers to have estimates of the size and extent of cheatgrass seedbanks in the planning and implementation of grazing pasture systems as well as in restoration planning and in understanding sites that are at risk of being converted to cheatgrass dominance. We describe through a bioassay system an approach at estimating cheatgrass seedbank densities at a variety of plant communities and characteristics to aid resource managers in estimating cheatgrass seedbanks.

Technical Abstract:
Cheatgrass (Bromus tectorum) is a highly invasive exotic annual grass that has invaded millions of acres of rangelands throughout the intermountain west. Cheatgrass out competes native perennial grass species for moisture, thus dominating the site under favorable conditions. Cheatgrass provides an early maturing fine textured fuel that increases the chance of ignition as well as the rate, spread and season of wildfires. Historically the sagebrush/bunchgrass rangelands of the intermountain west burned every 80-110 years. With the invasion of cheatgrass it is not uncommon to have fire intervals every 5-10 years, which is simply too short of a period of time to allow for the return of important shrub species. With each cheatgrass fueled wildfire, more and more important unburned islands are burned and converted to cheatgrass dominance. Grazing resources are lost as well as critical wildlife habitats. As little as 4 cheatgrass plants per square foot can out compete our more competitive perennial grasses, we have virtually hundreds of cheatgrass plants per square foot in many plant communities. We have measured cheatgrass densities in over 1,000 samples from more than 100 plant communities. These measurements averaged more than 250 cheatgrass plants per square foot that ranged from 0 to over 1,000, yet it is reported that as many as 3 times that amount of cheatgrass seed still remains in the seedbank. It is critical for resource managers to estimate the size and extent of seedbanks to better understand the dangers of this invasion as well as in the planning and implementation process of grazing management and restoration efforts. We try and provide a better understanding of approaching these critical estimates through a bioassay system of many plant communities with a variety of characteristics.